Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$81.32	5.593%	$85.8682	$85.87	$85.85	$85.90
Purchase #2	$62.98	10.145%	$69.3693	$69.37	$69.35	$69.40
Purchase #3	$169.30	11.682%	$189.0776	$189.08	$189.10	$189.10
Purchase #4	$139.42	13.575%	$158.3463	$158.35	$158.35	$158.30
Purchase #5	$85.79	4.408%	$89.5716	$89.57	$89.55	$89.60
Purchase #6	$15.56	10.675%	$17.221	$17.22	$17.20	$17.20
Purchase #7	$156.28	8.449%	$169.4841	$169.48	$169.50	$169.50
7 purchase totals =	$710.65		$778.9381	$778.94	$778.90	$779.00